Optimal harvest cluster size with increasing opening costs for harvest sites

In strategic level planning, the harvest levels are often obtained by maximizing NPV of the forest area. The resulting harvests within each planning period are then typically scattered over the area. In practical forestry, clustering harvests is seen as important, but tools for planning harvest clustering applicable for practical level planning are largely missing. In previous studies, clustering harvests has been seen as an objective in itself rather than means to save costs. It has thus not been possible to define an optimal level for clustering in order to maximize the NPV. In this study, clustering is carried out by minimizing the total opening costs (TOCs) for harvest sites. TOC is defined as a fixed cost for one contiguous harvest cluster. It consists of e.g. transferring the machines to the harvest site, waiting time for the machinery and workers due to the transfer, delineation of the harvest site and administrative work required for each harvest site. Our results show that with small opening cost, it is optimal to follow the strategic level plan, while as the opening cost increases it is optimal to make larger and larger harvest clusters. The clustering also affects the treatments carried out: with high opening costs the harvests in some stands will be postponed for 10years or more, or the treatment may change from the strategic level optimum.